U.S. patent number 7,616,735 [Application Number 11/728,927] was granted by the patent office on 2009-11-10 for tomosurgery.
This patent grant is currently assigned to Case Western Reserve University. Invention is credited to David Dean, Xiaoliang X. H. Hu, Robert Maciunas.
United States Patent |
7,616,735 |
Maciunas , et al. |
November 10, 2009 |
**Please see images for:
( Certificate of Correction ) ** |
Tomosurgery
Abstract
Systems, methods, and other embodiments associated with
Tomosurgery are described. One method embodiment includes logically
dividing a target volume into treatment slices to be radiated
individually by co-planar beams. The method embodiment also
includes planning a two dimensional path for moving a shaped
isocenter through a treatment slice where the isocenter is produced
by the intersection of the co-planar beams. The method embodiment
also includes planning a three dimensional path for moving the
shaped isocenter through the target volume based, at least in part,
on two dimensional paths. The method provides a signal to control a
radio surgery device to deliver radiation using the coplanar beams
to the target volume based, at least in part, on the three
dimensional path.
Inventors: |
Maciunas; Robert (Chesterland,
OH), Dean; David (Shaker Heights, OH), Hu; Xiaoliang X.
H. (New York, NY) |
Assignee: |
Case Western Reserve University
(Cleveland, OH)
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Family
ID: |
38821972 |
Appl.
No.: |
11/728,927 |
Filed: |
March 27, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070286343 A1 |
Dec 13, 2007 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60786457 |
Mar 28, 2006 |
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Current U.S.
Class: |
378/69;
378/65 |
Current CPC
Class: |
A61N
5/103 (20130101); A61N 5/1084 (20130101) |
Current International
Class: |
G21K
5/10 (20060101) |
Field of
Search: |
;378/65,69
;600/425,427 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Glick; Edward J
Assistant Examiner: Artman; Thomas R
Attorney, Agent or Firm: Kragul Jac + Kalnay, LLC
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application
60/786,457 titled Tomosurgery, filed Mar. 28, 2006, which is
incorporated herein.
Claims
What is claimed is:
1. A computer-implemented method, comprising: logically dividing a
target volume into two or more treatment slices to be radiated
individually by radiation delivered by co-planar beams; planning a
two dimensional path for moving a shaped isocenter through a
treatment slice, the two dimensional path to include a set of scan
points to be visited by the isocenter, the isocenter to be produced
by the intersection of the co-planar beams, and where planning a
first two dimensional path through a first treatment slice can
begin before a second treatment slice has been defined; planning a
three dimensional path for moving the shaped isocenter through the
target volume based) at least in part, on two or more of the two
dimensional paths; and providing a signal to control a radiosurgery
device to deliver radiation using the coplanar beams to the target
volume based, at least in part, on the three dimensional path.
2. The method of claim 1, including receiving one or more
pre-operative images in which at least a portion of the target
volume appears, the pre-operative images being one or more of,
magnetic resonance images, computed tomography images, and x-ray
images.
3. The method of claim 2, including fixing one or more fiducial
markers at a position relative to the target volume, where the
pre-operative images are to include representations of the one or
more fiducial markers; and where assembling, the three dimensional
plan depends, at least in part, on a relationship between an image
of a fiducial in a first treatment slice and an image of a fiducial
in a second treatment slice.
4. The method of claim 2, including fixing one or more fiducial
markers at a position relative to the target volume, where the
pre-operative images are to include representations of the one or
more fiducial markers; and where the delivery device is controlled,
at least in part, on determining a relationship between a portion
of the target volume and one or more of, a collimator opening, and
a radiation source.
5. The method of claim 1, where logically dividing the target
volume into two or more treatment slices includes determining a
treatment slice thickness.
6. The method of claim 1, a two dimensional path being a raster
scan path.
7. The method of claim 1, the shaped isocenter having a disk
shape.
8. The method of claim 1, where a shot weight produced by the
radiation delivered by the coplanar beams is modulated by
controlling the movement of the isocenter.
9. The method of claim 8, where the shot weight is modulated by
controlling one or more of, a number of coplanar beams applied to
the target volume, a hole size in a collimator through which at
least one of the coplanar beams is to pass, and a temporal delay
between one or more of the coplanar beams being applied to the
target volume.
10. The method of claim 1, where planning a two dimensional path
through a treatment slice includes calculating a resulting dose
according to:
.tau..function..times..times..function..times..tau..function.
##EQU00015## where D represents the resulting dose; where d
represents the disk-shaped shot dose kernel; where .tau. represents
a time series variable that represents the time it takes a moving
shot to pass through a unit length of a raster line; where m
represents a first index associated with a raster line scan point
position; and where n represents a second index associated with a
raster line scan point position.
11. The method of claim 10, where planning a two dimensional path
through a treatment slice includes solving for .tau. according to:
.function..tau..times..times..function..times..times..times..times..tau.
##EQU00016## where D.sub.i.sup.P is the prescribed dose for the
tumor; D.sub.i.sup.P is the planned dose distribution to be
optimized; and d.sub.ji of the dose kernel represents the dose
contribution to the i.sup.th spatial location while the shot moves
through the j.sup.th scan point.
12. The method of claim 11, where assembling the three dimensional
plan includes solving for a final three-dimensional plan dose
according to: .times. ##EQU00017## where D.sub.i.sup.S is the 3D
dose matrix; and w.sub.i is the weight assigned to the i.sup.th
single-plane raster scan.
13. The method of claim 1, where two dimensional paths through two
or more treatment slices are to be planned substantially in
parallel.
14. The method of claim 1, where two dimensional paths through two
different treatment slices differ in at least one of, scan pattern,
importance weighted quadratic objective function, and slice
orientation.
15. The method of claim 1, including controlling a delivery
apparatus to deliver a set of coplanar beams according to the three
dimensional plan.
16. The method of claim 15, including controlling the delivery
apparatus to deliver the coplanar beams to two or more treatment
slices substantially in parallel.
17. The method of claim 15, including: calibrating the delivery
apparatus before controlling the delivery apparatus to deliver the
coplanar beams; and controlling the delivery apparatus based, at
least in part, on the calibration.
18. The method of claim 17, where calibrating the delivery
apparatus includes acquiring a signal from a polymer gel-MRI
dosimeter to which the delivery apparatus applied a set of coplanar
beams.
19. The method of claim 1, including changing a tumor prescription
dose between planning a set of two dimensional paths and planning
the three dimensional path.
20. The method of claim 1, including dynamically altering the size
of a collimator hole through which at least one beam will pass
during radiation delivery to perform one or more of, modulating
shot weight, and controlling isocenter location.
21. The method of claim 1, including selecting a delivery apparatus
to deliver the coplanar beams based, at least in part, on the three
dimensional plan.
22. The method of claim 1 where planning the two dimensional path
includes considering a three dimensional dose bar interaction
within a treatment slice and where assembling the three dimensional
path includes considering a three dimensional dose bar interaction
between treatment slices.
23. A machine-readable medium having stored thereon machine
executable instructions that if executed by a machine cause the
machine to perform a method, the method comprising: receiving one
or more pre-operative images in which at least a portion of a
target volume to be radiated appears, the pre-operative images
being one or more of, magnetic resonance images, computed
tomography images, and x-ray images; determining a treatment slice
thickness; logically dividing the target volume into two or more
treatment slices to be radiated individually by radiation delivered
by co-planar beams, the treatment slices having the treatment slice
thickness; planning a two dimensional path for moving a disk-shaped
isocenter through a treatment slice, the two dimensional path to
include a set of scan points to be visited by the isocenter, the
isocenter to be produced by the intersection of the co-planar
beams, the two dimensional path being a raster scan path, where two
dimensional paths through two or more treatment slices are to be
planned substantially in parallel; planning a three dimensional
path for moving the shaped isocenter through the target volume
based, at least in part, on two or more of the two dimensional
paths, where a shot weight produced by the coplanar beams is
modulated by controlling the movement of the isocenter; providing a
signal to control a radiosurgery device to deliver radiation using
the coplanar beams to the target volume based, at least in part, on
the three dimensional path; and controlling a delivery apparatus to
deliver a set of coplanar beams according to the three dimensional
plan, where planning the two dimensional path includes considering
a three dimensional dose bar interaction within a treatment slice
and where assembling the three dimensional path includes
considering a three dimensional dose bar interaction between
treatment slices.
24. A radio surgical treatment method, comprising: identifying a
set of two dimensional paths through a set of treatment slices,
where planning a first two dimensional path through a first
treatment slice can begin before a second treatment slice has been
defined; receiving a treatment plan comprising a three dimensional
path through a target volume based, at least in part, on the set of
two dimensional paths; controlling a radio surgical apparatus to
generate a disk-shaped shot having an isocenter and to continuously
adjust the isocenter location to produce a coplanar shot movement
through the three dimensional path; and controlling the radio
surgical apparatus to modulate the speed at which the isocenter
location moves.
25. The method of claim 24, where modulating the speed at which the
isocenter location is moved includes controlling one or more
robotic apparatus associated with the radio surgical apparatus to
reposition one or more of, a patient, the radio surgical apparatus,
and a radiation source.
26. An apparatus, comprising: a first logic to partition a target
volume into a set of treatment slices, the target volume
representing a tissue to be subjected to radiation delivered by a
set of coplanar beams; a second logic to determine a set of two
dimensional raster scanning paths through the set of treatment
slices, where determining a first two dimensional raster scanning
path through a first treatment slice can begin before a second
treatment slice has been defined; a third logic to determine a
three dimensional path to irradiate the target volume to within a
pre-determined dose, the three dimensional path being based, at
least in part, on the set of two dimensional raster scanning paths;
and a fourth logic to control a delivery apparatus to deliver a set
of coplanar beams to the target volume in accordance with the three
dimensional path.
27. The apparatus of claim 26, the delivery apparatus being a
modified Leksell Gamma Knife.
28. The apparatus of claim 26, the delivery apparatus comprising: a
Linac unit with a collimator to shape radiation to a slit beam; a
ring-shaped secondary helmet with multiple collimator channels
through which multiple beams can focus to an isocenter to form a
disk-shaped shot; and a robotic positioning system that connects a
head frame to the ring-shaped secondary helmet.
29. The apparatus of claim 26, the delivery apparatus including a
rotating secondary apparatus.
30. The apparatus of claim 26, the delivery apparatus to rotate a
slit beam around a fixed portion of the delivery apparatus.
31. The apparatus of claim 26, including the delivery
apparatus.
32. The apparatus of claim 31, including a dosimeter to calibrate
the delivery apparatus.
33. The apparatus of claim 32, the first logic to receive a set of
pre-operative images in which the target volume is represented.
34. A system, comprising: means for identifying a set of treatment
slices in a target volume; means for planning a two dimensional
path through a treatment slice for a focused isocenter produced by
the intersection of coplanar radiation beams, where planning a
first two dimensional path through a first treatment slice can
begin before a second treatment slice has been defined; means for
assembling a three dimensional plan for performing radiosurgery on
the target volume, where the three dimensional plan depends, at
least in part, on a set of two dimensional paths through treatment
slices; and means for controlling a radiosurgery delivery apparatus
to move the intersection of the coplanar radiation beams through
the target volume according to the three dimensional plan.
Description
COPYRIGHT NOTICE
A portion of the disclosure of this patent document contains
material subject to copyright protection. The copyright owner has
no objection to the facsimile reproduction of the patent document
or the patent disclosure as it appears in the Patent and Trademark
Office patent file or records, but otherwise reserves all copyright
rights whatsoever.
BACKGROUND
Radiosurgery has typically been performed using a step-and-shoot
approach that delivers radiation according to a three dimensional
plan of multiple three dimensional shots. Multiple shots are
usually required to destroy the target pathology. Step and shoot
dose delivery involves repositioning the patient outside of the
irradiation field to reposition the centroid of the conformal
radiation dose. This type of radiosurgery has been time consuming
and may in some cases have produced sub-optimal results.
Radiosurgery may be performed using various devices. For example,
Leksell (Elektra, Stockholm, Sweden) provides a Gamma Knife.TM.
which may be referred to as an LGK. The LGK provides accurate
stereotactic radio surgical brain lesion treatment. The LGK derives
its therapeutic radiation from 201 60Co radiation sources. A
patient is exposed to these sources through pluggable collimator
channels. The radiation beams passing through unplugged collimator
channels focus in the center of a collimator helmet to create an
elliptically shaped conformal dose distribution. LGK shots are
traditionally elliptical due to the general shape of the human
skull. For a single shot, dose drop-off is steep at the boundaries
of this ellipse (e.g., 90% to 20% isodose). However, dose drop-off
steepness is diminished and made difficult to estimate when two or
more shots have overlapping dose distributions.
Shot planning seeks to achieve desired lesion coverage and killing.
However, shot packing is not as simple as filling a tumor, a
theoretical bag, with ellipses of dose. Planning multiple shots is
difficult due to the consequences of unintended intersections of
beams from different shots. These unintended intersections of beams
from different shots complicate treatment planning, and thus
lengthen the time required to plan a multi-shot treatment.
Furthermore, shot packing approaches typically cannot commence
until the entire pre-planning images are acquired.
Planning and delivery complexity are related to the geometric
complexity and volumetric complexity of a target volume. For
example, large lesion volume, complex lesion shape, and/or
complicated geometric relationships between the lesion and critical
structures complicate planning, and thus increase planning time and
increase the likelihood that suboptimal results will occur.
Conventional LGK treatment planning begins with a treatment
planning team that includes, for example, a neurosurgeon, a
radiation oncologist, and a radiation physicist. The treatment
planning team may survey pre-radio surgical images (e.g., CT, MR)
to locate the lesion in a series of adjacent 2D image slices.
Drawing the boundary of the lesion is referred to as
"segmentation". Other objects of interest, (e.g., critical
structures near the lesion), may also be segmented at this time.
Segmentation is typically performed manually using a contour
drawing tool. Shot packing strategies may not begin until the
entire set of image slices is available.
Conventional treatment planning falls into two categories: forward
treatment planning, and inverse treatment planning, with forward
treatment planning being the standard of care as of 2007. Treatment
planning begins with known parameters including prescribed dose,
lesion location, segmented tissue object contours, and so on.
Forward planning includes a trial-and-error approach for choosing
shot parameters including number of shots, shot positions,
collimator sizes, shot weights, and so on. As shot parameters are
selected the treatment planning team can calculate and evaluate the
sum of the radiation dose distribution. The treatment team will
then manually adjust setup parameters until an "acceptable"
treatment plan is obtained. This is an extremely technical and
manual process requiring the input of several highly skilled
personnel. This approach is not deterministic.
Given time limitations imposed by single session treatment a
significant issue for forward treatment planning is the relative
size of the search and solution space for acceptable treatment
plans. For a small lesion with a simple shape, forward planning may
perform adequately. The treatment planning team may place a shot in
the center of the target volume and then gradually add extra shots
to fill the under-dosed regions closer to the lesion surface.
However, the treatment plan search space increases dramatically
when a lesion has a large target volume, a complex target shape,
and/or a complex geometric relationship between the target volume
and nearby critical section (CS). In this situation, treatment
planning may require hours to obtain an acceptable treatment plan.
The shots resulting from this trial-and-error procedure may produce
unintended radiation dose overlap, particularly when multiple shots
are placed in close proximity.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate various example systems,
methods, and other embodiments of various aspects of the invention.
It will be appreciated that the illustrated element boundaries
(e.g., boxes, groups of boxes, or other shapes) in the figures
represent one example of the boundaries. One of ordinary skill in
the art will appreciate that in some embodiments one element may be
designed as multiple elements, multiple elements may be designed as
one element, an element shown as an internal component of another
element may be implemented as an external component and vice versa,
and so on. Furthermore, elements may not be drawn to scale.
FIG. 1 illustrates a portion of a three dimensional target volume
divided into a set of two dimensional treatment slices, which may
also be referred to as scanning planes.
FIG. 2 illustrates an example method associated with radiosurgery
planning.
FIG. 3 illustrates an example method associated with radiosurgery
planning and delivery.
FIG. 4 illustrates an example apparatus associated with
radiosurgery planning.
FIG. 5 illustrates an example apparatus associated with
radiosurgery planning and delivery.
FIG. 6 illustrates an example computing environment in which
example systems and methods illustrated herein may operate.
DETAILED DESCRIPTION
In one embodiment Tomosurgery involves slice based radiosurgery
that includes moving a high-precision, controlled-shaped isocenter
between scan points along a set of scanning lines in a portion of a
target volume divided into sets of treatment planes. In one
example, the scan points may be visited in a raster-scanning
pattern controlled by a set of 2D plans. Scan points may also be
visited slice by slice through a target volume as controlled by a
3D plan built from the set of 2D plans. The slice thickness may be
optimized to smooth peak-to-peak transitions between slices. Shot
weight can be adjusted by controlling parameters including, but not
limited to, shot movement speed, shot movement location, the number
of beams being used in the shot, the distance of the radiation
source from the target volume, and the size of beams used in the
shot. The number of beams and the size of the beams may be
determined by controlling on-the-fly collimator changes (e.g., plug
pattern, plug size), and/or by controlling a radiation source
position. The location of the isocenter can be moved by controlling
parameters including, but not limited to, the number of different
beams being used, temporal delays between beams, delivery apparatus
location and/or orientation, radiation source location, and/or
orientation, and patient location and/or orientation.
Tomosurgery seeks the precise and complete destruction of a chosen
target without significant unintended and/or unanticipated
concomitant damage to adjacent tissue. The radiation used in
Tomosurgery is ionizing high-energy beams that provide sufficient
energy to cause electrons to escape from the outer shell of atoms
in the target structure. The ionizing high-energy beams may radiate
from, for example, .sup.60Co. Cell death or injury may result from
DNA, cell membrane, and/or organellar damage.
Tomosurgery planning may include a two stage optimization where 2D
slices are solved and then a 3D assembly of 2D slices is solved. To
solve slices, the planning systems and methods need to have slices.
Thus, the 3D target volume is first identified and then partitioned
into 2D slices. The 3D target volume may be identified from images
including, for example, MR images, CT images, PET images, SPECT
images, X-rays, and so on. The 3D target volume may then be
logically "cut" into smaller pieces. In one example, the smaller
pieces are "slices" that can be considered to be two dimensional
surfaces over which a shot isocenter can be passed. The 2D surfaces
may be treated as a set of scan points lying in the same plane. The
2D projection images may be used to determine the placement of
raster lines that connect scan points and thus control desired dose
distribution in the first-stage optimization.
On these 2D projection images, tumor and CS regions may overlap.
Therefore, in one example, a set of rules may be used to control
placement of raster lines on a raster-scan plane. The rules may
include placing parallel raster lines sequentially along the y
direction, locating discrete scan points of each raster line only
within the tumor region in the corresponding projection image, and
not locating any discrete scan point within the projected CS
region. Using these rules facilitates determining the coordinates
(x, y, z) of the discrete scan points making up raster lines. In
one example, the final treatment plan is made up of a series of
scan points assigned with the optimized weight as controlled, for
example, by the speed of the moving shot.
While a "slice" is actually a three dimensional volume, it may be
treated as a two dimensional surface formed of a set of scan points
for planning and treatment purposes. In one example, multiple slice
orientations may be considered to provide multiple options for
solving the set of 2D problems. Additionally, in one example,
combinations of orientations may be considered to provide even more
options for solving the set of 2D problems. For example, a first
portion of a target volume may be sliced in a first orientation
while a second portion of a target volume may be sliced in a second
orientation. Solving slices arranged in different orientations may
be computationally expensive but may provide superior results for
target volumes that have particularly complicated geometries and/or
that interact with (e.g., wrap around) critical structure (CS) in
geometrically complex ways.
Tomosurgery may involve both parallel planning and parallel
delivery. Individual slices may be solved in parallel and may be
solved according to different strategies simultaneously. For
example, solutions that apply different importance functions and
different scanning patterns may be solved simultaneously so that
different options are available to attempt to solve the final 3D
assembly. Additionally, different solutions that involve delivering
a dose as a disk, an ellipse, or as another shaped shot may also be
computed in parallel to make even further options available for the
final 3D assembly. Additionally, different solutions that involve
controlling dose (in)homogeneity may be solved in parallel to
provide even further options for the final 3D assembly. Finally,
multiple 3D assemblies may be computed in parallel and an optimal
solution can be selected from the available plans. Different plans
may be more deliverable using different delivery devices. Thus,
part of the final 3D planning solution may include selecting a
delivery device for the plan. For example, a first 3D plan may be
optimized using a first delivery device (e.g., LGK) while a second
3D plan may be optimized using a second delivery device (e.g.,
medical LINAC).
Reduction to 2D slices and parallel delivery may be possible since
delivery apparatus (e.g., LGK) may be adaptable to provide a
substantially continuous dose using substantially coplanar beams
and/or sets of substantially coplanar beams. Using substantially
coplanar beams may facilitate reducing unintended beam
intersections which may in turn facilitate both simplifying
planning and delivering therapy in parallel.
Example systems and methods may perform intensity modulated
radiation therapy (IMRT) by modulating the speed of a moving shot
or moving shots. Dose can be controlled by how long a shot lingers
in a certain location. In one example, the moving shot(s) may be
disk-shaped, though other shot shapes may be employed. IMRT may
rely on achieving relative motion between a patient and a radiation
field to provide a planned radiation dose in a continuous fashion.
The relative motion may be achieved by moving the patient, by
moving the delivery apparatus, by moving the radiation source, and
by combinations thereof.
While some example systems and methods are described in association
with an LGK, the systems and methods are not so limited. For
example, treatment planning and radio-surgery may be associated
with other delivery mechanisms and radiation sources including, for
example, a cyberknife having a single point source of radiation, a
C arm linear accelerator, an apparatus having multi-leaf
collimators (MLC), and so on.
Similarly, while example systems and methods are described in
connection with brain surgery, the systems and methods are not so
limited. For example, treatment planning and radiosurgery may be
applied to other body parts including, for example, the torso,
extremities, and so on. Additionally, while the examples are
described in terms of human treatment, radiosurgery may be
performed on additional subjects (e.g., dogs, horses, cows).
Additionally, while example systems and methods describe a raster
based approached associated with a moving shot, it is to be
appreciated that other motion patterns may be employed. Raster
based approaches may simplify mechanical adaptations to
conventional apparatus and may facilitate simplifying motion plan
computations. However, in some examples, other motion plans (e.g.,
helical, spiral) for the moving shot may be employed.
In one embodiment, an LGK shot delivery mechanism dynamically moves
a shot isocenter to control dose homogeneity and/or dose
inhomogeneity. In one embodiment, an LGK plug-pattern that
facilitates selectively blocking collimators on an LGK helmet is
used. For example, all the collimators except those on a single
layer (e.g., lowest layer, most nearly coplanar row) are blocked.
This facilitates producing substantially coplanar beams. Thus, a
focused isocenter dose profile can be produced within a narrow
plane. The patient and/or field can be moved to make the plane
correspond to one of the 2D planes for which a raster plan has been
computed. The "shot" created by this plug-pattern may be a
disk-shaped distribution of lethal radiation (e.g., a shot).
References to "one embodiment", "an embodiment", "one example", "an
example", and so on, indicate that the embodiment(s) or example(s)
so described may include a particular feature, structure,
characteristic, property, element, or limitation, but that not
every embodiment or example necessarily includes that particular
feature, structure, characteristic, property, element or
limitation. Furthermore, repeated use of the phrase "in one
embodiment" does not necessarily refer to the same embodiment,
though it may.
The following includes definitions of selected terms employed
herein. The definitions include various examples and/or forms of
components that fall within the scope of a term and that may be
used for implementation. The examples are not intended to be
limiting. Both singular and plural forms of terms may be within the
definitions.
"Machine-readable medium", as used herein, refers to a medium that
participates in directly or indirectly providing signals,
instructions and/or data that can be read by a machine (e.g.,
computer). A machine-readable medium may take forms, including, but
not limited to, non-volatile media (e.g., optical disk, magnetic
disk), and volatile media (e.g., semiconductor memory, dynamic
memory). Common forms of machine-readable mediums include floppy
disks, hard disks, magnetic tapes, RAM (Random Access Memory), ROM
(Read Only Memory), CD-ROM (Compact Disk ROM), and so on.
"Data store", as used herein, refers to a physical and/or logical
entity that can store data. A data store may be, for example, a
database, a table, a file, a list, a queue, a heap, a memory, a
register, a disk, and so on. In different examples a data store may
reside in one logical and/or physical entity and/or may be
distributed between multiple logical and/or physical entities.
"Logic", as used herein, includes but is not limited to hardware,
firmware, executing instructions, and/or combinations thereof to
perform a function(s) or an action(s), and/or to cause a function
or action from another logic, method, and/or system. Logic may
include a software controlled microprocessor, discrete logic (e.g.,
application specific integrated circuit (ASIC)), an analog circuit,
a digital circuit, a programmed logic device, a memory device
containing instructions, and so on. Logic may include a gate(s), a
combinations of gates, other circuit components, and so on. Where
multiple logical logics are described, it may be possible in some
examples to incorporate the multiple logical logics into one
physical logic. Similarly, where a single logical logic is
described, it may be possible in some examples to distribute that
single logical logic between multiple physical logics.
An "operable connection", or a connection by which entities are
"operably connected", is one in which signals, physical
communications, and/or logical communications may be sent and/or
received. An operable connection may include a physical interface,
an electrical interface, and/or a data interface. An operable
connection may include differing combinations of interfaces and/or
connections sufficient to allow operable control. For example, two
entities can be operably connected to communicate signals to each
other directly or through one or more intermediate entities (e.g.,
processor, operating system, logic, software). Logical and/or
physical communication channels can be used to create an operable
connection.
"Signal", as used herein, includes but is not limited to,
electrical signals, optical signals, analog signals, digital
signals, data, computer instructions, processor instructions,
messages, a bit, a bit stream, or other means that can be received,
transmitted and/or detected.
"Software", as used herein, includes but is not limited to, one or
more executing computer instructions that temporarily transform a
general purpose machine into a special purpose machine. Software
causes a computer, processor, or other electronic device to perform
functions, actions and/or behave in a desired manner. Software may
be embodied in various forms including routines, algorithms,
modules, methods, threads, and/or programs. In different examples,
software may be implemented in executable and/or loadable forms
including, but not limited to, a stand-alone program, an object, a
function (local and/or remote), a servelet, an applet, instructions
stored in a memory, part of an operating system, and so on. In
different examples, computer-readable and/or executable
instructions may be located in one logic and/or distributed between
multiple communicating, co-operating, and/or parallel processing
logics and thus may be loaded and/or executed in serial, parallel,
massively parallel and other manners.
"User", as used herein, includes but is not limited to, one or more
persons, software, computers or other devices, or combinations of
these.
Some portions of the detailed descriptions that follow are
presented in terms of algorithm descriptions and representations of
operations on electrical and/or magnetic signals capable of being
stored, transferred, combined, compared, and otherwise manipulated
in hardware. These are used by those skilled in the art to convey
the substance of their work to others. An algorithm is here, and
generally, conceived to be a sequence of operations that produce a
result. The operations may include physical manipulations of
physical quantities. The manipulations may produce a transitory
physical change like that in an electromagnetic transmission
signal.
It has proven convenient at times, principally for reasons of
common usage, to refer to these electrical and/or magnetic signals
as bits, values, elements, symbols, characters, terms, numbers, and
so on. These and similar terms are associated with appropriate
physical quantities and are merely convenient labels applied to
these quantities. Unless specifically stated otherwise, it is
appreciated that throughout the description, terms including
processing, computing, calculating, determining, displaying,
automatically performing an action, and so on, refer to actions and
processes of a computer system, logic, processor, or similar
electronic device that manipulates and transforms data represented
as physical (electric, electronic, magnetic) quantities.
FIG. 1 illustrates a portion 100 of three dimensional target volume
that has been logically partitioned into a set of two dimensional
treatment slices. In one embodiment, Tomosurgery involves
continuously delivering a radiation dose with dynamic intensity
modulation performed temporarily, spatially, or both in accordance
with a 3D plan derived from a set of 2D plans developed for the set
of treatment slices. The radiation may be delivered to a set of
scan points arranged along a set of scan lines (e.g., 191, 192, . .
. 199) that correspond to treatment lines 110, 111, . . . 119 in
portion 100. The spatial intensity modulation may be achieved by
moving the center of a shot, which may be achieved by causing
relative motion between a patient, a delivery apparatus, and/or a
radiation source.
In one embodiment, a continuous LGK shot delivery mechanism may
dynamically move a shot isocenter to control dose homogeneity. The
LGK may be configured to deliver dose continuously with a modulated
shot radiation dose level moving at modifiable speeds along
suitable pathways in accordance with the set of 2D plans to improve
both dose conformality and normal tissue sparing. The 2D plans may
be solved independently and in parallel to reduce planning time.
The 2D planning problems may include varied-speed shot movement to
improve dose conformality.
The 2D plans may then be assembled into a 3D plan. Once again,
segments of the 3D plan can be assembled in parallel. Consider a 3D
volume sliced into 256 2D slices for planning. In one example, some
or all of the 256 2D slices may be solved in parallel.
Additionally, some or all of the 256 2D slices may be solved using
different parameters (e.g., importance functions, scan plans).
Plans for the 256 2D slices may then be assembled into a 3D plan.
Once again, multiple 3D plans may be computed in parallel and a
most optimal solution chosen at the end. In one example, 16
separate process may be tasked with assembling sets of 16 slices in
parallel. In another example, 128 process may assemble sets of
adjacent slices, then 64 processes may assemble sets of four slice
assemblies, and so on. Larger subsets of slices may then ultimately
be assembled into the final 3D model.
With one 3D plan made up of multiple 2D slices, in one example
radiation may be delivered to treat different slices in parallel.
Parallel radiation delivery within isolated treatment slices
facilitates reducing therapy delivery time. Improvements in dose
conformality and homogeneity may also improve radiosurgery for
larger-volume and/or more geometrically complex lesions.
Example systems and methods may control a delivery apparatus to
produce a disk-like shot using a delivery apparatus that produces a
nearly planar dose. These systems and methods may rely on a kinetic
equation that describes a "3D dose bar" radiation distribution when
this disk-like shot moves through a lesion in each treatment slice
in, for example, a raster scanning fashion.
Example systems and methods may consider the characteristics of the
3D dose bar, consider the interaction between adjacent 3D dose bars
in the same slice (e.g., inter-raster line dose), and consider the
interaction between two slices (e.g., inter-slice dose). Example
systems and methods may also consider dose interaction and
inhomogeneity resulting from changing dose bar velocity. Example
systems and methods may use information concerning disk-like shot
radiation dose distribution to automatically generate an inverse
treatment plan that includes modulated velocity.
In one example, Tomosurgery inverse treatment planning involves a
two-stage optimization strategy utilizing an importance-weighted
quadratic objective function and iterative least-square
minimization. The resulting delivery causes a shot to move
continuously through a target volume (e.g., lesion) delivering
tumoricidal radiation to a series of adjacent slices in a
raster-scan format. So long as relative motion between the target
volume and the irradiation field is possible, continuous motion of
the radiation dose is possible.
The inverse treatment planning is to be performed in a clinically
relevant and acceptable time frame to provide improved plan quality
and application to different radiation therapy modalities. Moving
the high-precision shaped isocenter relies on being able to produce
relative motion between a target volume and an irradiation field.
The relative motion may be achieved using positioning units
associated with the patient, the delivery apparatus, the radiation
source, and so on. For example, equipping an LGK with two
positioning units, each of which has three computer controlled
motors, may facilitate continuously changing the position of the
shot isocenter.
As described above, pre-operative 3D MR-scanning, LGK treatment
planning, and LGK radiosurgery may need to be accomplished in a
single work session. Thus, time is of the essence. The single
session is conventionally mandated because the rigid stereotactic
frame is affixed to a patient's skull. This fixed length of time
may lead to compromises between manual treatment planning and the
radiosurgery procedure in complex cases. While conventional systems
tend to wait until the entire 3D MR-scan is complete, some example
systems can start solving some individual 2D slices as soon as they
are available, further reducing overall planning and thus session
time. In some cases, 3D pre-operative imaging, tomosurgery
planning, and radiation delivery may be separated into different
sessions that do not need to be completed in a single session by
the use of fiducials that may be affixed to the target volume
and/or to anatomy that will maintain a constant relationship to the
target volume in between imaging, planning, and delivery. For
example, a set of three fiducials that are highly visible to MR
imaging may be affixed to a patient skull in a pre-determined
pattern and used subsequently in planning and/or delivery.
For a treatment slice, the central transverse plane may be referred
to as the "raster-scan plane" in which the disk-shaped shot moves
in a raster format. The treatment slices may have an optimal slice
thickness. In one example, the slice-scan nature of the Tomosurgery
paradigm is understood by analyzing dose distribution for a
constant-speed moving disk-shaped shot in the form of linear scan,
single-plane raster scan and multi-plane raster scan. Analyzing
dose distribution by linear scan (moving shot along a straight
line) facilitates obtaining the optimal slice thickness. Analyzing
single-plane and multi-plane raster scans facilitates understanding
dose distribution, including approximated dose drop-off steepness
and isodose contour width. The following discussion illustrates the
analysis.
In one example, a disk-shaped shot is generated using a helmet
plug-pattern having the upper four layers of a commercially
available collimator closed with only a fifth layer open. This
approximates coplanar beams. In the example, the voxel size of the
161.times.161.times.161 3D matrix that stores the dose kernel is
0.25.times.0.25.times.0.25 mm.sup.3. Different dose kernels for
available collimator sizes (e.g., 4 mm, 8 mm, 14 mm, 18 mm) may be
calculated. In one example, a 4 mm collimator is used since smaller
shots increase the likelihood of achieving greater dose
conformality.
Given a disk-shaped dose kernel matrix d and a moving speed related
variable v(x) at the location x, a dose distribution D due to a
linear scan along the x axis can be expressed according to:
.function.'.times..function.'.times..function.' ##EQU00001##
where {circle around (x)} is the convolution operator. For disk
movement performed with discrete steps, v(x) is a shot-weight
series. In one example, the speed may be treated as a constant and
the .sup.60Co can be assumed not to decay. In this example,
equation (1) simplifies to:
.function.'.times..function.' ##EQU00002##
If the straight line along which the disk-shaped shot moves is
considered to be infinitely long, then the example can ignore the
regions close to the start and end points. Therefore, D can be
treated as a bar-shaped compressed cylinder and the dose profile on
a cross-sectional plane (y-z) of the 3D dose bar will be the same,
(e.g., D(x.sub.1, y, z)=D(x.sub.2, y, z) for arbitrary x.sub.1 and
x.sub.2). Therefore, the cross-sectional dose profile of the 3D
dose bar can be denoted as D.sub.cs(y, z) for purposes of
simplification.
Given D.sub.cs(y, z) as the cross-sectional dose profile of the 3D
dose bar, define D.sub.cs(y=0, z) as the function .phi., which is
approximately symmetrical by z=0. In one embodiment, planning may
depend on previously determining the similarity between .phi. and
D.sub.cs(y, z) at arbitrary y fixed and determining the optimal
offset for two shifted .phi. functions so that their summation has
the flattest/smoothest peak-to-peak transition. For the sum of two
shifted bell-shaped functions, such as F(x)+F(x+offset), the
peak-to-peak transition represents the curve between the peaks of
F(x) and F(x+offset).
Because the correlation coefficient is independent of origin and
scale, it may be used to evaluate the similarity of D.sub.cs(y, z)
to .phi. at different fixed y. The correlation coefficient has the
value between 0 and 1. The complete correlation has the correlation
coefficient equal 1.
The pre-determining may include searching for an optimal offset for
which the sum of two shifted .phi. functions has the smoothest
peak-to-peak transition. Given two shifted .phi. functions,
.phi.(z) and .phi.(z-l.sub.o), define H.sub.l.sub.o(z) as:
H.sub.l.sub.o(z)=c.PHI.(z)+.PHI.(z-l.sub.o), c.epsilon.[0.5, 1]
(3)
where c is a constant and l.sub.o is the offset between those two
shifted .phi. functions. When c equals 1, a horizontal line from
peak to peak (z .epsilon. [0, l.sub.o]) is desired to present the
most smoothness. When c is less than 1, a non-horizontal straight
line is expected to ideally reach the most smoothness. To quantify
the smoothness, define the smoothness as the average of the
unsigned curvature of the given curve segment (peak-to-peak
transition). The unsigned curvature .kappa. in this case can be
given as:
.kappa..function..differential..function..differential..times..differenti-
al..function..differential. ##EQU00003##
The predetermining may also include calculating .kappa. in discrete
form. By focusing on peak-to-peak smoothness for a particular
region (e.g., the curve segment of H.sub.l.sub.o(z) when
0.ltoreq.z.ltoreq.l.sub.o), the peak-to-peak smoothness
C.sub.s(l.sub.o) can be presented as the arithmetic mean of the
curvature in discrete:
.function..times..times..kappa. ##EQU00004##
where the peak-to-peak curve segment of H.sub.l.sub.o(z) is
represented by N discrete points. Because the curvature measures
the failure of a curve to be a straight line and the curvature of a
regular straight vanishes if that straight line is not horizontal,
the smoothest peak to peak transition will be obtained when
C.sub.s(l.sub.o) tends to zero.
The predetermining may also include analyzing 3D dose bars derived
from clinical cases. The analysis may include searching the optimal
offset l.sub.o where C.sub.s(l.sub.o) is minimum for different c
value in H.sub.l.sub.o(z), such as c=0.5, 0.6, 0.7, 0.8, 0.9, and
1. The shot dose kernel matrix used has the voxel size at
0.25.times.0.25.times.0.25 mm.sup.3.
In one example system, the planar raster scan may be performed on a
transverse plane (x-y). A single-plane raster scan may be made up
of multiple parallel linear scans on the same plane. A multi-plane
raster scan can be formed from a stack of single-plane raster
scans. While a single-plane raster scan is described, it is to be
appreciated that other scanning patterns may be employed (e.g.,
spiral, helical).
The cross-sectional dose profile D.sub.cs(y, z) of a single 3D dose
bar is approximately mirror-symmetrical along either z or y axis.
The minimal and mean correlation coefficient is no less than 0.977
and 0.991 respectively. Therefore, D.sub.cs(y, z) has substantially
the same function form as .phi. at any y value, but different
scale. Thus, D.sub.cs(y, z) can be expressed at arbitrary y as:
D.sub.cs(y,z)=D.sub.cs(y,0).PHI.(z), at arbitrary y (6)
The single-plane raster scan can be regarded as the alignment of
multiple parallel 3D dose bars centered by the same plane in a
raster format where each raster line is the axial of the respective
3D dose bar. Dose distribution delivered by a single-plane raster
scan can be approximated as a sum of multiple .phi. functions with
varied scale along any longitudinal line (parallel with z axis) in
dose space regardless of inter-raster line distance. Assume the
single-plane raster scan has N raster lines and the inter-raster
line distance is l.sub.a. The dose distribution for this
single-plane raster scan on a cross-sectional plane can be
presented as D.sub.sps(y, z):
.function..times..function..times..function..PHI..function..PHI..function-
..times..times..function. ##EQU00005##
Note that D.sub.cs(y+(n-1)l.sub.a,0) is a constant. Therefore, for
the single-plane raster scan the dose profile along a longitudinal
line D.sub.sps(y,z) at arbitrary y fixed, will reserve the function
form of .phi. but has varied scale determined by:
.times..function. ##EQU00006##
In one example, an optimal offset for .phi. may exist. In the
provisional application, this optimal offset was seen at 4.01 mm.
Even while c in the H.sub.l.sub.o function was not 1, the optimal
offset was still 4.01 mm. Thus, the optimal offset value may be
universally valid so that the smoothest dose transition by the
multi-plane raster scan along any longitudinal line can be reached
if the treatment slice thickness equals the optimal offset.
Therefore, by choosing the treatment slice thickness to be the same
as the optimal offset, a multi-plane raster scan in the raster
format by a disk-shaped shot will generate smooth dose transition
around treatment slice junctions instead of unexpected dose
overlapping due to hard-to-predict beam intersections/overlapping,
and divide the lesion into the least number of treatment slices
without sacrificing dose homogeneity inside the lesion.
In the experiments described in the provisional application, the
FWHM values (4.01 mm) were close to the optimal offset values for
all cases and therefore may be used to approximate the optimal
treatment slice thickness directly. H.sub.l.sub.o may be defined as
a weighted sum of two shifted .phi. functions corresponding to the
scenario with the two raster lines per single-plane raster scan
instead of multiple shifted .phi. functions associated with the
more general cases with several raster lines per single-plane
raster scan. For multiple shifted .phi. functions with the same
optimal offset value the overlapped dose will still have the
smooth/flat transition from peak to peak since .phi. has the very
steep drop-off so that one .phi. function has minimal impact on
another .phi. function that is far enough away.
A lesion volume might not be exactly divided by the optimal
treatment slice thickness, leaving a portion of a lesion undivided.
When the offset value l.sub.o increases outside a pre-defined
range, the profile of H.sub.l.sub.o between the peaks of two
overlapped .phi. functions varies from a hill to a platform and
then to a valley. If the optimal offset value cannot be used, then
a smaller H.sub.l.sub.o is favored because a larger H.sub.l.sub.o
may lead to under-dosed peak-to-peak transition.
Example systems and methods may use single-plane raster scanning to
create elliptical isodose contours on cross-sectional planes.
Example systems and methods may then extend to multi-plane raster
scanning by stacking multiple single-plane raster scans. Example
systems and methods may rely on the dose overlapping effect in
situations where one treatment slice is smaller than another. This
facilitates creating a dose conformal to the lesion volume if the
cut-off cross-sectional geometrical shape of a lesion has
continuous and roughly 1.sup.st order linear change within a
pre-defined thickness. Therefore, example systems and methods may
consider the dose distribution on the mid-plane of a treatment
slice, which can be planned as a 2D problem. After assembling
(e.g., stacking) individually planned treatment slices, the
overlapped dose from slice to slice will conform to the lesion
geometric changes from one treatment slice to another. Therefore,
the original 3D planning problem is converted to a series of 2D
planning problems that can be individually solved without 3D,
convolution, which means planning time can be reduced. Planning
time can be reduced even further because the individual 2D planning
problems may be solved in parallel and planning may begin even
before the entire 3D MR image is acquired. 2D solutions may then be
stacked into the 3D plan, with the stacking occurring in parallel.
In some examples, different approaches to solving the individual 2D
planning problems may be undertaken in parallel with optimal
solutions being selected from the results of the different
approaches. Similarly, different approaches to solving the 3D
assembly problem may be undertaken in parallel with an optimal
solution being selected from the different solutions.
Example systems and methods may consider how isodose contours vary
while applying different scan formats. The number of single-plane
raster scans affects the width of isodose contours along the
longitudinal z direction only. Thus, stacking multiple single-plane
raster scans having an optimal treatment slice thickness does not
worsen the dose spread-out within each treatment slice itself and
will proportionally expand isodose contours/surfaces along
longitudinal z direction. Therefore, single-plane raster scanning
can be seen as individually filling a dose within a corresponding
treatment slice.
In example systems and methods, modulating shot speed facilitates
improving conformality of the dose to the target lesion. In example
systems and methods, a Tomosurgery treatment plan includes a series
of raster lines that include a series of discrete scan spots/stops
where the moving shot will stay. A time-factor is assigned to a
scan spot and represents how long the moving shot takes passing
through. Assuming an undecayed radiation source, this time-factor
is analogous to shot weight.
In one example, Tomosurgery treatment planning first determines the
location of a series of adjacent treatment slices that cover the
entire lesion volume. Second, the 3D volumes for tissue types
(e.g., lesion, CS, normal tissue (NT)) within each treatment slice
are projected to the central transverse plane of that treatment
slice. In one example, the disk-shaped Tomosurgery shot dose
profile at .gtoreq.50% isodose is approximately the same thickness
as each treatment slice and therefore the treatment plan can be
solved for a 2D projection view of each treatment slice. Thus, 2D
plan optimizations involve 2D convolution, which can be performed
more quickly than 3D convolution. Third, the 3D dose distribution
of optimized 2D plans are calculated. These 3D dose distributions
are assembled (e.g., stacked) longitudinally to create the final 3D
plan.
Example systems and methods may consider how to orient treatment
slices. It is computationally simplest if the treatment slices are
parallel to the original MR-based x-y plane. In this case treatment
slice thickness can be measured along the longitudinal z axis. The
lesion thickness may, or more likely may not be fully divisible by
the optimal treatment slice thickness.
A 2D plan may manage a single-plane raster scan by the moving
disk-shaped shot. Dose level in each treatment slice may increase
slightly after the 3D treatment plan is directly assembled. A
target volume (e.g., lesion) may not be exactly divisible into
slices of the optimal thickness. Thus, there may be a remaining
undivided portion of target volume thickness. Therefore, example
systems and methods may organize an additional treatment slice that
covers the undivided lesion portion that is partially overlapping
with the first or the last slice previously divided out. For these
two partially overlapped slices, assembling the corresponding 2D
plans will not yield a smooth/flat peak to peak transition.
In some examples, treatment slices may have a transverse (x-y)
orientation, the same orientation as an original MR slice data.
Other example systems and methods are not so limited. In one
example, a target volume may be serially sectioned into treatment
slices along the pre-determined longitudinal z direction. The
central transverse plane of a treatment slice is referred to as
"raster-scan plane" onto which the disk-shaped moving shot may be
aligned.
Given an overall tumor volume thickness T along the longitudinal
direction (e.g., the z direction) and an optimal treatment slice
thickness T.sub.opt, the division of the tumor volume can be
determined, in one example, using the following expression:
T=T.sub.opt.times.N+R (3-1)
There are two possible situations: 1) R=0, where T can be exactly
divided by T.sub.opt and 2) R.noteq.0, where T cannot be exactly
divided by T.sub.opt and the remaining undivided portion of the
tumor volume has a thickness<T.sub.opt. For both of these
situations, the corresponding central transverse planes of the
initial N treatment slices may be chosen as the raster-scan planes
so that the distance between two adjacent raster-scan planes is
T.sub.opt. If the tumor volume is completely filled by these
treatment slices (R=0), the procedure can conclude. If the tumor
volume can not be filled completely (R.noteq.0), an extra
raster-scan plane (N+1.sup.th) may be appended. However, the
distance between the last two raster-scan planes (N.sup.th and
N+1.sup.th) is R instead of T.sub.opt. In an example described in
the provisional application, T.sub.opt is 4 mm for the use of a 4
mm collimator. It is to be appreciated that for other collimator
sizes other optimal slice thicknesses may be employed. For the
raster-scan planes, a serial raster line may be used as the path
for the moving disk-shaped dose.
In one example, z.sub.s, the position of a raster-scan plane is
recorded along the z direction. The volumes of different tissue
types within the range of z.sub.s.+-.X mm may be projected onto the
corresponding raster-scan plane. These 2D tissue projections are
used to determine the desired dose distribution in the first-stage
optimization. The 2D projections of both the tumor and CS may be
saved separately while the regions without tumors or CS may be
regarded as NT. Overlap of the 2D tissue projections for tumors and
CS is possible in some situations. Given the 2D tissue projection
for a raster-scan plane, the rules described above can be applied
to place the raster lines. The rules facilitate determining the
coordinates (x, y, z) of these scan points making up the raster
lines.
Using a disk-shaped dose kernel and a set of scan points
representing the raster lines, the resulting dose can be calculated
using:
.tau..function..times..times..function..times..tau..function..times..time-
s. ##EQU00007##
where .tau. represents a time series variable that represents the
time it takes the "moving shot" to pass through a "unit length" of
each raster line. More specifically, .tau. is the shot weight in
the terminology of the conventional LGK, and, finally, d is the
disk-shaped shot dose kernel.
In one example, both optimization stages may use a similar
quadratic objective function and importance-weighted iterative
least-square minimization. Adjustment of the prescribed dose or the
importance factors can push a treatment plan via this optimization
towards a desired result. In one example, the prescribed dose for
each case may be adjusted to control the average dose in the entire
tumor volume. The importance ratio may be emphasized to match
planned dose distribution to desired dose distribution for one
(e.g., tumor only) or two (e.g., tumor plus CS) tissue types.
An importance-weighted objective function may be used to solve for
.tau.:
.function..tau..times..times..function..times..times..times..times..tau..-
times..times. ##EQU00008##
where D.sub.i.sup.p is the prescribed dose for the tumor, NT, and
CS, D.sub.i.sup.d is the planned dose distribution to be optimized,
d.sub.ji of the dose kernel represents the dose contribution to the
i.sup.th spatial location while the shot moves through the j.sup.th
scan point. Because the slice information may be projected to the
corresponding raster-scan plane, the dose calculation at this stage
is a 2D convolution operation that uses the central transverse
plane of d.sub.ji. l.sub.i is the predefined importance factor of
each tissue type assigned to the i.sup.th spatial location. The
projection results in tumor and CS may overlap and thus there may
be a location on a 2D projection where both a tumor and a CS
appear. Therefore, one example may treat the cost of Eq. (3-3) as
the sum of the contributions from all three tissue types. Eq. (3-3)
is a convex problem that may be solved using an iterative
least-square minimization based on the following iterative
equation:
.tau..tau..function..times..times..times..times..times..times..times.
##EQU00009## The solution space search is guided by an "update"
factor that is the ratio between the prescribed dose and the
calculated dose from the previous iteration.
In one example, it may be possible to fix the normalized
prescription dose to 0.8 for tumor, 0.2 for NT, and 0.2 for CS.
Given n 2D treatment plans produced by the first-stage
optimization, the assembly of the final 3D plan dose distribution
(D.sub.f) is performed by weighting these n 2D plans according
to:
.times..times..times. ##EQU00010##
where D.sub.i.sup.s is the 3D dose matrix saving the dose
distribution by the i.sup.th single-plane raster scan (e.g., the 2D
treatment plan), and is calculated based on Eq. (3-2); w.sub.i is
the weight assigned to the i.sup.th single-plane raster scan and
the variable to be solved by the second-stage optimization. If
w.sub.i=1, there is no adjustment to the i.sup.th planar scan. A
large change of w.sub.i from 1 means that there is a large
adjustment.
The dose distribution for a single-plane raster scan has steep dose
drop-off along the longitudinal z direction. Therefore, one example
may limit the thickness of the dose matrix D.sub.i.sup.s to
3.times.T.sub.opt, to save computation time. An importance-weighted
objective function similar to Eq. (3-3) and an iterative equation
similar to Eq. (3-4), derive the second stage optimization
presented in Eqs. (3-6) and (3-7), respectively:
.function..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times.
##EQU00011## where l is the importance factor assigned to each
tissue type; w is a vector of size n, the number of the 2D
treatment plans. In this second-stage optimization, one example may
fix the normalized tolerance dose at 0.2 for NT, and adjust the
prescription dose for tumor tissue virtually by a trial-and-error
approach that depends on both tumor volume and whether CS is
present. Adjustment away from the prescribed tumor dose may occur
as a trade-off between in-tumor average dose and dose conformality.
A highly conformal dose in a small tumor may be closer to the
original prescribed dose (e.g., relatively higher) than in a large
tumor. In one example, the importance ratios of tumor:NT:CS may be
set the same in the second-stage optimization as in the
first-stage. After the second-stage optimization, the time-series
.tau. of each 2D treatment plan may be adjusted by multiplying the
corresponding weight w.sub.i in order to get the final, optimized,
3D LGK Tomosurgery treatment plan.
In one example, the first-stage optimization of each 2D slice
treatment plan can be limited to a pre-determined, configurable
number of iterations (e.g., 50). In one example, second stage
weight adjustments may be made. A large weight adjustment may occur
on the last two 2D treatment plans because of the partial overlap
of the last two treatment slices, and a small weight adjustment may
occur on the treatment slices nearest the tumor central transverse
plane. To get the final 3D plan, .tau. of each 2D treatment plan
may be multiplied by the corresponding weight w.sub.i.
In one example, second-stage optimization may be limited to a
pre-determined, configurable number of iterations (e.g., 5). A
smaller number of iterations may be employed since complex 3D
convolution calculations may be reduced. This also provides
treatment planning time improvements over conventional methods.
After first-stage optimization, the time-series .tau. is extended
(e.g., the shot lingers) near the tumor boundary and smoothly
decreases its value (e.g., increases the speed) as the disk-shaped
shot progresses toward to the tumor center. Also, the optimal value
of .tau. tends to be less variable in this central area. The
optimization algorithm seeks to match the planned dose distribution
to this desired flat dose distribution. Near the tumor boundary,
the reduction in adjacent raster lines results in reduced, dose
contributions. As a result, raster lines near the tumor boundary
optimally have a boosted dose that compensates for the reduction in
adjacent scan lines. In the center of the tumor, raster lines have
a similar number of nearby scan lines. Thus .tau. is approximately
constant to create the desired constant dose distribution by the
optimization. Each optimized single-plane raster scan by the
corresponding 2D plan has the desired flat "dose pie" enclosed by
the 50% prescription isodose surface.
The second-stage optimization may adjust 2D treatment plans during
the 3D plan assembly. The last two slices (e.g., end slice and next
to end slice) often have the scanning planes closer to each other
than the other adjacent slices and thus the dose transition between
them has a higher amplitude with a hill profile. Dose weighting
adjustments are determined by factors like the total length of each
raster line in the current treatment slice and in the nearby
treatment slices, the longitudinal position of each raster-scan
plane, and the number of all raster-scan planes.
The tumor prescription dose may be changed in the second-stage
optimization so that the average in-tumor dose is not too high.
Making modest changes in the prescribed dose during the
optimization facilitates improving dose homogeneity and/or
conformality. Dose conformality and CS survival may be closely
coupled since they may be mutually exclusive goals.
Tomosurgery may employ various delivery apparatus that produce
high-accuracy focal radiation dose delivery in the form of a
moving, disk-shaped isocenter that results from the intersection of
multiple beamlets. The apparatus may employ a rigid yet mobile
frame-based patient localization device supporting dynamic dose
delivery via a moving isocenter. In one example, an existing LGK
may be modified.
One example platform includes a medical Linac.TM. (Varian
Associates, Palo Alto, Calif.) mounted with a multi-leaf collimator
(MLC). The Peacock.TM. system (NOMOS Corporation, Sewickley, Pa.)
is one commercially available, MLC-mounted system. The Linac can
shape radiation to a slit (fan) beam. The platform may include an
optional ring-shaped secondary helmet with multiple collimator
channels through which multiple beams can focus to an isocenter
mimicking an LGK Tomosurgery disk-shaped shot, and a high-accuracy
robotic positioning system that connects a head frame to the
ring-shaped secondary helmet.
In one example, a delivery apparatus could include a secondary
helmet that includes a solid bowl or cylindrical tube with a
ring-shaped base. This secondary helmet may be placed on a
high-precision computer-controlled rotary table, so that it can
rotate with an expected, controllable angular velocity. The base of
the rotary secondary helmet may have multiple collimator channels
that shape radiation beams received from an externally slit beam
into multiple temporally delayed small beamlets. These beamlets,
which may be temporally delayed due to the rotation of the helmet,
focus to create a disk-shaped isocenter dose. A stereotactic (head)
frame may be attached to this helmet through an automatic phantom
positioning system similar to the APS of the LGK model C.
Example systems and methods may interact with a calibration unit.
In a polymer gel-MRI dosimeter, a polymer gel may be formulated by
dispersing monomer into an aqueous gel matrix. Irradiated polymer
gel will present a different T2 relaxation rate than non-irradiated
polymer. Therefore, following irradiation, a T2-weighted 3D MR
image of the gel-based phantom may be used to report the absorbed
dose distribution. For a specific gel formulation, the relationship
between absorbed dose distribution and R2 (1/T2) weighted map may
be assumed to be linear within a suitable range. Compared with
other radiosurgery/radiotherapy dosimeters, the polymer gel-MRI
method provides high resolution 3D dose distribution data. Once a
polymer gel-MRI dosimeter has been calibrated, it can be used to
verify the dose delivery accuracy of a Tomosurgery procedure. To
increase the co-registration accuracy of the treatment plan and the
dosimeter 3D MR image of the delivered dose, multi-modality
fiducial markers may be employed.
PABIG (polyethylene glycol diacrylate, N,N'-methylenebisacrylamide,
gelatin) gel formulation may be used with the dosimeter. An MR-scan
of the irradiated gel-based phantom may use a volume selective
32-echo Carr-Purcell-Meiboom-Gill pulse sequence (e.g., TE1, TE2, .
. . , TE32=40 ms, 80 ms, . . . , 1280 ms, TR of 2.3 s,
reconstructed voxel size of 1.times.1.times.1 mm.sup.3) with phase
encoding being applied in two orthogonal directions and Fourier
interpolation taking place in the slice reconstruction direction.
The readout T.sub.2 matrix includes the reconstructed slices
converted to an R.sub.2 (1/T.sub.2) matrix. The calibration curve
of the PABIG gel preparation is obtained by linearly fitting
R.sub.2 values in the dose range of 0-35 Gy through the following
equation: R.sub.2(D)=.alpha.D+R.sub.2(0) (5-1)
where .alpha. is the dose sensitivity value and D is the dose
level. Then, the calibration curve is normalized. The dose
delivered to the phantom may be obtained using the same MRI pulse
sequence.
Dosimetry may include acquiring two images, a pre-operative (e.g.,
pre-irradiation) and a post-operative (e.g., post-irradiation) MRI
scan of the phantom. The pre-operative MRI scan may be performed by
using a spoiled T.sub.1-weighted 3D-fast field echo (FFE) sequence.
The pre-operative MRI image may be input to the treatment planning
algorithm which simulates the Tomosurgery procedure. The
post-operative MRI scan may be based on the same MRI sequence used
in the gel-MRI dosimeter calibration scan. The MRI readout may be
converted to a R.sub.2 matrix and then converted to a normalized
dose (percentage) based on the calibration curve.
To deliver radiation to an isocenter with an accurate distribution
and weight, an apparatus may include a portion that rotates
continuously with a known, controllable, angular velocity. A fixed
slit beam (20 cm.times.2 cm) may irradiate the rotating secondary
ring collimator with the phantom attached internally. In one
example, delivering x-y planar symmetrical radiation at each
isocenter may be simplified by using a 360 degree rotation of the
collimator helmet with a constant angular velocity. Given fixed
Linac output power, and a constant angular velocity for the rotary
collimator helmet, the dose rate detected at the isocenter may be
deterministic. The radiation beams passing through the collimator
channels of the secondary helmet may be analyzed and characterized
using a gel-MRI dosimeter. Then, a dose kernel calculation model
may be used to match the setup. Then, the relationship of the
delivered isocenter dose rate to the angular velocity of the rotary
helmet may be obtained. The knowledge of this relationship (ref.
Eq. (5-2)) facilitates transferring the Tomosurgery treatment plan
to other dose delivery plans.
Based on the Tomosurgery treatment planning algorithm described
above, a final treatment plan may be made up of a series of scan
points assigned with the optimized weight (speed). Given fixed
Linac output power, the shot moving speed (weight) may be converted
to the corresponding angular velocity of the rotary helmet based on
the simplified equation:
.omega..times..times..pi..eta..function..times..times.
##EQU00012##
where .omega..sub.i represents the angular velocity of the rotary
helmet to deliver the isocenter shot to the i.sup.th scan point; w
is the weight (shot speed) assigned to a scan point; .eta. is a
function of w describing the dose rate converted from the shot
speed; and, D.sub.d is the desired dose to be delivered. For this
simplified equation, factors and coefficients relevant to the
radiation physics is implicitly modeled by the function .eta.. The
model .eta. and the dose kernel calculation model may be specific
to the radiation source and the secondary helmet design.
To translate the Tomosurgery paradigm to the LGK, there are at
least two options: 1) replacing the original manufacturer
components with an automatic positioning system based on a pair of
Cartesian robots; or 2) not only changing the positioning system,
but also changing the secondary helmet and the placement of
radiation sources. In one example, only the fifth-layer collimator
channels (44 totally corresponding to 44 Cobalt-60 sources) are
opened. Thus, the dose rate is lower than that of a plug pattern
with all collimator channels (201 totally) opening. The dose rate
could be increased if a customized secondary helmet was used. Thus,
it may be possible to increase the number of or change the shape of
collimator channels in a customized secondary helmet. The number of
Cobalt-60 sources could also be increased. Note that the collimator
orientation of the current secondary helmet does not allow beamlets
to conform in a coplanar fashion. Therefore, in one example, in an
LGK dedicated to Tomosurgery, the number of Cobalt-60 sources may
be increased and the secondary collimator helmet may be modified to
provide only coplanar radiation beams.
Motorized control of a multi-leaf blocker (MLB) may be implemented
using a series of parallel leaves that may be individually
controlled. These leaves may slide in/out to turn on/off an
underneath collimator channel on-the-fly during the treatment
delivery, allowing for more flexible dose shaping (e.g.,
conformality). Thus, a computer-controlled MLB system may allow
more complex treatment delivery including dose shaping and steeper
dose drop-off, thereby significantly reducing the dose to which
normal and critical structures would be exposed. An automated MLB
may provide on-the-fly collimator diameter shifts while being
assisted by correctly positioning the main body of the secondary
helmet.
Having described the science and engineering of Tomosurgery, the
following description of the figures illustrate example methods and
systems for planning and performing Tomosurgery. FIG. 2 illustrates
an example method 200 associated with Tomosurgery planning. FIG. 3
illustrates an example method 300 associated with Tomosurgery
planning and delivery.
Example methods may be better appreciated with reference to flow
diagrams. While for purposes of simplicity of explanation, the
illustrated methods are shown and described as a series of blocks,
it is to be appreciated that the methods are not limited by the
order of the blocks, as in different embodiments some blocks may
occur in different orders and/or concurrently with other blocks
from that shown and described. Moreover, less than all the
illustrated blocks may be required to implement an example method.
In some examples, blocks may be combined, separated into multiple
components, may employ additional, not illustrated blocks, and so
on. In some examples, blocks may be implemented in logic. In other
examples, processing blocks may represent functions and/or actions
performed by functionally equivalent circuits (e.g., an analog
circuit, a digital signal processor circuit, an application
specific integrated circuit (ASIC)), or other logic device. Blocks
may represent executable instructions that cause a computer,
processor, and/or logic device to respond, to perform an action(s),
to change states, and/or to make decisions. While the figures
illustrate various actions occurring in serial, it is to be
appreciated that in some examples various actions could occur
concurrently, substantially in parallel, and/or at substantially
different points in time.
Method 200 may include, at 210, logically dividing a target volume
to be radiated into treatment slices. These treatment slices may
then be individually radiated. In one example, before logically
dividing the target volume into treatment slices, method 200 will
determine a treatment slice thickness.
Method 200 may also include, at 220, planning a two dimensional
path for moving a shaped isocenter through a treatment slice. The
isocenter will be produced at the intersection of co-planar beams.
Since a target volume may be divided into a set of treatment
slices, the planning at 220 may occur for multiple slices. In one
example, the shaped isocenter for which the path will be planned
will have a disk shape. In one example, the two dimensional path
will include a set of scan points to be visited by the isocenter.
In one example, the two dimensional path will be a raster scan
path. In one example, planning a two dimensional path through a
treatment slice includes calculating a resulting dose according to
equations described above. Similarly, planning a two dimensional
path through a treatment slice may include solving for .tau.
according to equations described above.
Method 200 may also include, at 230, planning a three dimensional
path for moving the shaped isocenter through the target volume
based, at least in part, on two or more of the two dimensional
paths. In one example, a shot weight produced by the coplanar beams
is modulated by controlling the movement of the isocenter. In
addition to moving the isocenter, shot weight may be modulated by
controlling one or more of, a number of coplanar beams applied to
the target volume, a hole size in a collimator through which at
least one of the coplanar beams is to pass, and a temporal delay
between one or more of the coplanar beams applied to the target
volume. In one example, assembling the three dimensional plan may
include solving for a final three-dimensional plan dose according
to equations described above.
Method 200 may also include, at 240, providing a signal to control
a radiosurgery device to deliver radiation using the coplanar beams
to the target volume based, at least in part, on the three
dimensional path. Providing the signal may include, for example,
generating an interrupt, sending a data packet, controlling the
voltage on a control line, providing a file that includes path
data, providing executable instructions, and so on.
In one example, two dimensional paths through treatment slices are
to be planned substantially in parallel. In one example, two
dimensional paths through different treatment slices may differ in
at least one of, scan pattern, importance weighted quadratic
objective function, and slice orientation. Additionally, in one
example, planning a first two dimensional path through a first
treatment slice may begin before a second treatment slice has been
defined. The three dimensional plan may reveal issues that went
unobserved during two dimensional planning. Thus, method 200 may
also include changing a tumor prescription dose between planning
two dimensional paths and planning the three dimensional path.
In one example, method 200 may also include receiving a
pre-operative image(s). The pre-operative image may include a
representation of at least a portion of the target volume. Thus,
the logical dividing at 210 may include analyzing the pre-operative
images. The pre-operative images may be, for example, magnetic
resonance images, computed tomography (CT) images, x-ray images,
and so on.
Method 300 may include some actions similar to those described in
connection with FIG. 2. For example, method 300 may include the
logical dividing at 310, the 2D path planning at 320, the 3D path
planning at 330, and providing a control signal at 340. However,
method 300 may also include additional actions.
Consider that the delivery apparatus may be dynamically
controllable. Control may be exercised for example, over radiation
source distance, over the number of collimator openings, over the
size of collimator openings, and so on. In one example, control may
be done on-the-fly. Thus, method 300 may include, at 350,
controlling a delivery apparatus to deliver a set of coplanar beams
according to the three dimensional plan. Controlling the delivery
apparatus may include, for example, controlling the delivery
apparatus to deliver the coplanar beams to two or more treatment
slices substantially in parallel. Controlling the delivery
apparatus may also include, for example, controlling the opening
and closing of collimator holes, controlling the angular velocity
of a rotating radiation source, controlling the angular velocity of
a rotating blocking device, and so on.
The delivery apparatus may provide radiation from radiation
sources. Radiation sources may decay over time. Therefore, to
improve treatment, method 300 may also include calibrating the
delivery apparatus before controlling the delivery apparatus to
deliver the radiation using the coplanar beams. With the
calibration data acquired, method 300 may also include controlling
the delivery apparatus based, at least in part, on the calibration.
Calibrating the delivery apparatus may include, for example,
acquiring a signal from a polymer gel-MRI dosimeter to which the
delivery apparatus applied a set of coplanar beams.
Method 300 may also include, in one example, selecting a delivery
apparatus to deliver the coplanar beams based, at least in part, on
the three dimensional plan.
Method 200 and/or method 300 may also include fixing a fiducial
marker(s) at a position relative to the target volume. Thus,
pre-operative images will include representations of the fiducial
markers. Alternatively, method 200 and/or method 300 may simply
include receiving pre-operative images that include representations
of the fiducials. With the fiducials placed and visible, assembling
the three dimensional plan may depend, in one example, on a
relationship between an image of a fiducial in a first treatment
slice and an image of a fiducial in a second treatment slice.
Similarly, with the fiducials placed and visible, control of the
delivery device may depend, at least in part, on determining a
relationship between a portion of the target volume and another
item (e.g., a collimator opening, a radiation source). Use of these
fiducials may free example systems from constraints associated with
fixed stereotactic frames and/or single session
imaging/planning/delivery.
While FIGS. 2 and 3 illustrates various actions occurring in
serial, it is to be appreciated that various actions illustrated in
these figures could occur substantially in parallel. By way of
illustration, a first process could logically divide a target
volume, a second process could perform 2D planning and a third
process could perform 3D planning. While three processes are
described, it is to be appreciated that a greater and/or lesser
number of processes could be employed and that lightweight
processes, regular processes, threads, and other approaches could
be employed.
FIG. 4 illustrates an example apparatus 400 associated with
Tomosurgery planning. Apparatus 400 may include a first logic
(e.g., partition logic 410) to logically partition a target volume
into a set of treatment slices. The target volume represents a
tissue to be subjected to radiation surgery. The radiation may be
delivered by a set of coplanar beams. The radiation may be
delivered from fixed radiation sources and/or from radiation
sources that may move (e.g., circularly) about a target volume.
Apparatus 400 may also include a second logic (e.g., 2D logic 420)
to determine a set of two dimensional raster scanning paths through
the set of treatment slices. The determining may proceed in
accordance with the methods and equations described above. The
determining may account for whether the path is to be created from
fixed radiation sources and/or from moveable (e.g., rotating)
sources.
Apparatus 400 may also include a third logic (e.g., 3D logic 430)
to determine a three dimensional plan to irradiate the target
volume to within a pre-determined dose. As described above, the
three dimensional plan is to be based, at least in part, on the set
of two dimensional raster scanning paths. Once again the
determining may account for whether the path is to be created from
fixed radiation sources and/or from moveable (e.g., rotating)
sources. Apparatus 400 may also include a fourth logic (e.g.,
control logic 440) to control a delivery apparatus to deliver
radiation in a set of coplanar beams to the target volume. The
delivery will be made in accordance with the three dimensional
path. The control logic 440 may generate a set of signals that are
provided to a delivery apparatus. The signals may take different
forms, though an electrical signal is preferred.
FIG. 5 illustrates an example apparatus 500 associated with
Tomosurgery planning and delivery. Apparatus 500 includes elements
similar to those described in connection with apparatus 400. For
example, apparatus 500 includes a partition logic 510, a 2D logic
520, a 3D logic 530, and a control logic 540. Additionally,
apparatus 500 includes a delivery apparatus 550. In one example the
delivery apparatus 550 may be a modified Leksell Gamma Knife.
In one example, the delivery apparatus 550 may be a Linac unit with
a collimator to shape radiation to a slit beam. The delivery
apparatus 550 may include a ring-shaped secondary helmet with
multiple collimator channels through which multiple beams can focus
to an isocenter to form a disk-shaped shot. The delivery apparatus
550 may also include a robotic positioning system that connects a
head frame to the ring-shaped secondary helmet. While a head frame
and a "helmet" are described, it is to be appreciated that the
delivery apparatus 550 may be modified to facilitate Tomosurgery to
body parts other than the head. It is to be appreciated that
delivery apparatus 550 may be other devices that are capable of
producing a substantially planar shot and moving the isocenter of
that shot through a treatment slice according to a 2D plan. For
example, the delivery apparatus 550 may include a rotating
secondary apparatus and/or may include elements to rotate a slit
beam around a fixed portion of the delivery apparatus.
Since a radiation source(s) may decay, apparatus 500 may include a
dosimeter to calibrate the delivery apparatus. In one example, the
partition logic 510 may include a logic to receive a set of
pre-operative images in which the target volume is represented. The
partition logic 510 may then automatically partition the target
volume into treatment slices.
FIG. 6 illustrates an example computing device in which example
systems and methods described herein, and equivalents, may operate.
The example computing device may be a computer 600 that includes a
processor 602, a memo 604, and input/output ports 610 operably
connected by a bus 608. In one example, the computer 600 may
include a Tomosurgery logic 630 configured to facilitate planning
for Tomosurgery and delivering radiation according to a Tomosurgery
plan. In different examples, the logic 630 may be implemented in
hardware, software, firmware, and/or combinations thereof. Thus,
the logic 630 may provide means (e.g., hardware, software,
firmware) for identifying a set of treatment slices in a target
volume and means (e.g., hardware, software, firmware) for planning
a two dimensional path through a treatment slice. Logic 630 may
also provide means (e.g., hardware, software, firmware) for
assembling a three dimensional plan for performing radio-surgery on
the target volume, and means (e.g., hardware, software, firmware)
for controlling a radiosurgery delivery apparatus to move the
intersection of the coplanar radiation beams through the target
volume according to the three dimensional plan. While the logic 630
is illustrated as a hardware component attached to the bus 608, it
is to be appreciated that in one example, the logic 630 could be
implemented in the processor 602.
The means described in connection with logic 630 may determine an
optimal slice thickness using the following inputs, algorithms, and
outputs.
Input:
Calculated 3D dose kernel d of a disk-shaped shot.
Origin/center of d(x, y, z) set to (0, 0, 0).
Algorithm:
(1) Calculate the cross-sectional dose profile Dcs of the 3D dose
bar by projecting d (x, y, z) to y-z plane. Here, Dcs is a function
of y and z.
(2) Find the FWHM of Dcs(y=0, z).
Output:
The FWHM approximately equals to the optimal treatment slice
thickness, Topt.
The means described in connection with logic 630 may interpolate
the 3D volume data of segmented tumor and critical section (CS)
using the following inputs, algorithms, and outputs.
Input:
Binary (BW) volume data of segmented tumor and CS, as Vt and Vcs
respectively. Sizes of Vt and Vcs, Dim_t and Dim_cs, and their
voxel sizes, VOXS_t and VOXS_cs. Real volume values.
Algorithm:
(1) Use cubic interpolation to resample Vt and Vcs to the smaller
voxels, 0.25.times.0.25.times.0.25 mm.sup.3..fwdarw.grayscale
volume data, VI_t and VI_cs, which have the enlarged dimensions
than the original volume sizes (Dim_t and Dim_cs). (2) Use 3D
smoothing kernel to smooth VI_t and VI_cs.fwdarw.VS_t and VS_cs.
(3) Find the best threshold TH_OPT where the thresholded tumor
volume and CS volume close to the real volumes. The search of the
best threshold can be performed through binary search approach: a.
Testing the middle of an interval (initially 0-1) b. Eliminating a
half of that interval c. Repeating the procedures a-c on the other
half of that interval. Termination condition: the difference
between the old and new threshold values<the pre-defined
tolerance value. (4) Perform thresholding on VI_t and VI_cs by
using the threshold TH_OPT. Output: Binary volume data for
resampled tumor and CS, VO_t and VO_cs.
The means described in connection with logic 630 may determine a
raster scan format using the following inputs, algorithms, and
outputs.
Input:
Tumor and CS volume data, VO_t, and VO_cs.
Tumor volume thickness T and the optimal treatment slice thickness
Topt.
Algorithm:
(1) Based on equation T=Topt.times.N+R, calculate R and N. (2)
Divide the tumor volume along the z direction to a serial N
adjacent treatment slices (with the thickness as Topt) starting
from the superior side. The middle x-y plane of each treatment
slice is the corresponding raster-scan plane. The locations of the
raster-scan planes in z are recorded in an N-sized array, raster_z.
(3) If R=0, go to (4); otherwise, append a new entry onto the array
raster_z (now, the array size becomes N+1). The value of new entry,
raster_z(N+1)=raster_z(N)+R. The total number of the raster-scan
planes is denoted as n (=N or N+1). (4) For each treatment slice,
project tumor tissues and CS tissues onto the corresponding
raster-scan plane. The projected images are denoted as Proj_t and
Proj_cs for tumor and CS tissues respectively. (5) Place the raster
lines within the tumor projection regions but not in the CS
projection regions. Record the location of each raster-scan point
into the array raster_points(x, y, z). Output: The locations of
raster-scan points, raster_points array.
The means described in connection with logic 630 may perform a
first stage optimization using the following inputs, algorithms,
and outputs.
Input:
raster_points array.
Tumor and CS volume data, VO_t and VO_cs.
Prescribed dose for tumor, PRESCRIPTION_DOSE=1.
Dose tolerance of normal tissues (NT), TOLERANCE_NT=0.2.
Dose tolerance of CS, TOLERANCE_CS=0.2.
Important factors to tumor, NT, and CS, IF_T, IF_NT, and IF_CS.
Virtually adjusted prescribed dose, VPD (fixed to 0.8 here).
Algorithm:
.tau..tau..times..times..times..times..times. ##EQU00013## (1)
Calculate .tau. for raster points based on the iterative equation.
(2) Terminate iterative procedure when the tumor killing ratio
becomes worse. Output: Array raster_weight, which records .tau. of
each raster point.
The means described in connection with logic 630 may pre-process
for the second stage optimization using the following inputs,
algorithms, and outputs.
Input:
Arrays, raster_weight and raster_points.
Shot dose kernel d.
Algorithm:
For the i-th treatment slice:
(1) Allocate computer memory DS(i) as a 3D matrix. DS(i) has the
thickness of 3.times.Topt in z. (2) Calculate the 3D dose
distribution resulted from the i-th planar raster scanning. The
resulted dose distribution is saved into DS(i). The dose
distribution is calculated based on 3D convolution of d and
raster_weight. Output: Totally n DS matrices.
The means described in connection with logic 630 may perform a
second stage optimization using the following inputs, algorithms,
and outputs.
Input:
n DS matrices.
Arrays raster_weight and raster_points.
Tumor and CS volume data, VO_t and VO_cs.
Prescribed dose for tumor, PRESCRIPTION_DOSE=1.
Dose tolerance of normal tissues (NT), TOLERANCE_NT=0.2.
Dose tolerance of CS, TOLERANCE_CS=0.2.
Important factors to tumor, NT, and CS, IF_T, IF_NT, and IF_CS.
Virtually adjusted prescribed dose, VPD.
Algorithm:
.times..times..times..times..times. ##EQU00014## (1) Calculate w
for each treatment slice based on the iterative equation. (2)
Terminate iterative procedure when the tumor killing ratio and CS
survival (if applicable) becomes worse. (3) For each treatment
slice, adjusting the shot speed:
raster_weight=raster_weight.times.w. Output: The adjusted
raster_weight array. The adjusted shot weights (speed) can now be
used to calculate the dose distribution of the final treatment
plan.
Generally describing an example configuration of the computer 600,
the processor 602 may be a variety of various processors including
dual microprocessor and other multi-processor architectures. A
memory 604 may include volatile memory and/or non-volatile memory.
Non-volatile memory may include, for example, ROM, PROM, EPROM, and
EEPROM. Volatile memory may include, for example, RAM, synchronous
RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double
data rate SDRAM (DDR SDRAM), and direct RAM bus RAM (DRRAM).
A disk 606 may be operably connected to the computer 600 via, for
example, an input/output interface (e.g., card, device) 618 and an
input/output port 610. The disk 606 may be, for example, a magnetic
disk drive, a solid state disk drive, a floppy disk drive, a tape
drive, a Zip drive, a flash memory card, and/or a memory stick.
Furthermore, the disk 606 may be a CD-ROM, a CD recordable drive
(CD-R drive), a CD rewriteable drive (CD-RW drive), and/or a
digital video ROM drive (DVD ROM). The memory 604 can store a
process 614 and/or a data 616, for example. The disk 606 and/or the
memory 604 can store an operating system that controls and
allocates resources of the computer 600.
The bus 608 may be a single internal bus interconnect architecture
and/or other bus or mesh architectures. While a single bus is
illustrated, it is to be appreciated that the computer 600 may
communicate with various devices, logics, and peripherals using
other busses (e.g., PCIE, SATA, Infiniband, 1394, USB, Ethernet).
The bus 608 can be types including, for example, a memory bus, a
memory controller, a peripheral bus, an external bus, a crossbar
switch, and/or a local bus.
The computer 600 may interact with input/output devices via the i/o
interfaces 618 and the input/output ports 610. Input/output devices
may be, for example, a keyboard, a microphone, a pointing and
selection device, cameras, video cards, displays, the disk 606, the
network devices 620, and so on. The input/output ports 610 may
include, for example, serial ports, parallel ports, and USB
ports.
The computer 600 can operate in a network environment and thus may
be connected to the network devices 620 via the i/o interfaces 618,
and/or the i/o ports 610. Through the network devices 620, the
computer 600 may interact with a network. Through the network, the
computer 600 may be logically connected to remote computers.
Networks with which the computer 600 may interact include, but are
not limited to, a local area network (LAN), a wide area network
(WAN), and other networks.
To the extent that the term "includes" or "including" is employed
in the detailed description or the claims, it is intended to be
inclusive in a manner similar to the term "comprising" as that term
is interpreted when employed as a transitional word in a claim.
Furthermore, to the extent that the term "or" is employed in the
detailed description or claims (e.g., A or B) it is intended to
mean "A or B or both". The term "and/or" is used in the same
manner, meaning "A or B or both". When the applicants intend to
indicate "only A or B but not both" then the term "only A or B but
not both" will be employed. Thus, use of the term "or" herein is
the inclusive, and not the exclusive use. See, Bryan A. Garner, A
Dictionary of Modern Legal Usage 624 (2d. Ed. 1995).
To the extent that the phrase "one or more of, A, B, and C" is
employed herein, (e.g., a data store configured to store one or
more of, A, B, and C) it is intended to convey the set of
possibilities A, B, C, AB, AC, BC, and/or ABC (e.g., the data store
may store only A, only B, only C, A&B, A&C, B&C, and/or
A&B&C). It is not intended to require one of A, one of B,
and one of C. When the applicants intend to indicate "at least one
of A, at least one of B, and at least one of C", then the phrasing
"at least one of A, at least one of B, and at least one of C" will
be employed.
* * * * *